科研之友
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摘要
The weighted mean temperature T-m is a variable parameter in the Global Navigation Satellite System (GNSS) meteorology and the Askne-Nordius zenith wet delay (ZWD) model. Some parameters about the T-m seasonal variation (e.g. the annual mean value, the annual range, the annual and semi-annual amplitudes, and the long-term trend) were discussed before. In this study, some additional results about the T-m seasonal variation on a global scale were found by using the T-m time series at 309 global radiosonde sites. Periodic signals of the annual and semi-annual variations were detected in these T-m time series by using the Lomb-Scargle periodogram. The annual variation is the main component of the periodic T-m in non-tropical regions, while the annual variation or the semiannual variation can be the main component of the periodic T-m in tropics. The mean annual T-m almost keeps constant with the increasing latitude in tropics, while it decreases with the increasing latitude in non-tropical regions. From a global perspective, T-m has an increasing trend of 0.22 K/decade on average, which may be caused by the global warming effects. The annual phase is almost found in about January for the non-tropical regions of the Southern Hemisphere and in about July for the non-tropical regions of the Northern Hemisphere, but it has no clear symmetry in tropics. Unlike the annual phase, the geographical distributions of semi-annual phase do not follow obvious rules. In non-tropical regions, the maximum and minimum T-m of the seasonal model are usually found in respective summer and winter days while the maximum and minimum T-m are distributed over a whole year but not in any fixed seasons for tropical regions. The seasonal model errors increase with the increasing value of annual amplitude. A primary reason for the irregular seasonal variation in tropics is that T-m has rather small variations in this region.
- 出版日期2017-12-1
- 单位东南大学
